Ensure that Googlebot-Mobile gets redirected to mobile.

* The case-insensitive non-greedy match wasn't working and is tricky to read.
* Removal of "bot" from the original regex will ensure that Google-Mobilebot
is redirected appropriately because "mobi" is included in the User-Agent string.
* Removal of "bot" from the original regex is nondestructive, as there aren't
other bots that also have "mobi" or other mobile-identifying keywords in their
UA string that are accessing the desktop URLs under /wiki/.

Change-Id: I0739bc99b717b5de2e9b178a58225be865f0d0a7